FOOD MICROBIOLGY I
2nd week Microorganisms in foods and their functions Microorganisms in foods can be divided into four groups according to their functions: . Spoilage microorganisms . They cause to lost of quality and economical values of food when their levels are 106 /g-cm2 or more. . Microorganisms that have beneficial functions . Some microorganisms, such as lactic acid bacteria used as starter culture, provide desirable changes in taste, odor or structure of food. . Microorganisms that harmful to health . Intoxication . Infection . Inert microorganisms that have neither useful nor harmful functions in foods.
Bacteria Acetobacter . Gram (-), non-sporeforming, aerobic, catalase (+) rods. Some species are motile while some are non-motile . Acetobacter is a genus of acetic acid bacteria characterized by the ability to convert alcohol (ethanol) to acetic acid in the presence of oxygen. There are several species within this genus, and there are other bacteria capable of forming acetic acid under various conditions; but all of the Acetobacter are known by this characteristic ability. . Acetobacter are of particular importance commercially, because: . they are used in the production of vinegar (intentionally converting the ethanol in the wine to acetic acid); . they can destroy wine which they infect by producing excessive amounts of acetic acid or ethyl acetate, both of which can render the wine unpalatable; . they are used to intentionally acidify beer during long maturation periods in the production of traditional Flemish Sour Ales; . A. xylinum is the main source of microbial cellulose. . Some species, which produce excessive mucus substrates such as Acetobacter xylinum, can cause blockage of vinegar generators, so can cause problems in vinegar production. Aeromonas . Members of these genus are Gram (-), facultative anaerobic, oxydase (+), motile rods. . They are found normally in intestinal flora and then can be contaminated foods by fecal materials. . Fourteen species of Aeromonas have been described, most of which have been associated with human diseases. . Two major diseases associated with Aeromonas are gastroenteritis and wound infections, with or without bacteremia1). Gastroenteritis typically occurs after the ingestion of contaminated water or food, whereas wound infections result from exposure to contaminated water. 1)Bacteremia is the presence of bacteria in the blood. The blood is normally a sterile environment, so the detection of bacteria in the blood (most commonly with blood cultures) is always abnormal.
Alcaligenes . They are aerobic, Gram(+) but sometimes Gram (-) rods (sometimes cocci or cocobacilli). They don’t produce pigments. . They can be found in soil, water, dust, raw milk, poultry meats and fecal material. o . Optimum growth temperature: 20-37 C . They cause putrefactive spoilage of fresh meat. Alicyclobacillus . They are thermo-acidophilic, obligate aerobic and sporeforming bacteria. . Thermophilic acidophilic spore-forming bacteria Alicyclobacillus can grow at low pH and at moderately high temperatures such as 40°C. . This genus consist of three species: . A. acidocaldarius, A. acidoterrestris and A. cycloheptanicus. . They can be found in soil and hot springs. . Some of the species are known to cause spoilage of acidic beverages and produce medicinal odors. However, they do not produce gas or cause any change in the appearance of the beverage container, and therefore the spoilage is discovered only when the consumer opens and begins to consume the product. . Fortunately, Alicyclobacillus are not pathogenic bacteria, but they are troublesome, not only for consumers but also for beverage producers, because no effective control methods have yet been developed.
Arcobacter . Arcobacter genus has Campylobacter-like bacteria and firstly identified as aerotolerant campylobacters. . They are Gram (-), spiral shaped, aerotolerant and motile with a single polar flagellum. . Habitats of Arcobacter species are cattle, pigs, poultry and primates. . They can cause abortion in cattle and pigs. Also, they can cause bacteremia, endocartidis, peritonitis and enteritis in humans. . The most important species pathogenic for human is A. butzleri. Endocarditis: A bacterial infection of the endothelium (heart’s inner lining) Peritonitis: inflammation of the peritoneum, inflammation of the membrane that lines the abdominal cavity (Medicine) Bacillus . Members of this genus are Gram (+), aerobic or facultative anaerobic, spore-forming rods. . Bacillus antracis (anthrax) . B. thuringiensis (insect pathogen) . B. cereus (food-borne disease) . B. coagulans and B. stearothermophilus can grow at pH values as low as 4.2 and cause spoilage of canned foods. . B. stearothermophilus spores are the most resistant bacterial spores. . B. subtilis produce a bacteriocin called subtilin. . B. licheniformis: bacitracin, B. polymxa:polymixin . B. subtilis, B. amiloliquefaciens and B. stearothermophilus are used for production of bacterial α-amylase. . B. subtilis, B. mesentericus and B. stearothermophilus are used for bacterial proteinase. This enzyme is used for tenderization of meat and fish as well as to stabilize the protein turbidity in wine and beer industry.
Brucella . These bacteria are Gram (-), non-motile, aerobic cocobacilli or short rods. . Three species are the cause of brucellosis in different animals. This disease can result in abortion in pregnant animals. . Brucellosis can be seen also in humans. It is transmitted by ingesting infected food, direct contact with an infected animal, or inhalation of aerosols. Minimum infectious exposure is between 10 – 100 organisms. Brucellosis primarily occurs through occupational exposure (e.g. exposure to cattle, sheep, pigs), but also by consumption of unpasteurized milk products. . Raw meat, sausages, fermented sausages and pastırma are the other sources. Campylobacter . Gram (-), motile, non-capsulated, non-sporeforming, curved rods. . Their main source is poultry meats. . Additionally, they can be isolated from fecal materials, domestic animals, seafood, fruits and vegetables. . When they were first isolated, they classified in Vibrio genus. But then named as Campylobacter that means “curved rod” and classified under Campylobacteriacea family.
Carnobacterium . Gram (+), catalase (-) rods . This genus contain some strains which classified formerly in Lactobacillus genus. . They can be isolated form vacuum-packaged meats, fish products and poultry meats. Citrobacter . Gram (-), motile with peritrichous flagella. . All species of this genus can use citrate as carbon source. . Their main source is intestinal tract and can be found in foods. . The most important species is C. freundii. . Citrobacters are also members of coliform group bacteria that are indicators microorganisms.
Clostridium . Gram (+), anaerobic, spore-forming rods. . They are used as sterilization indicator. . C. botulinum: botulism . C. tetani: Tetanus . C. perfringens: formerly called C. welchii, causes a wide range of symptoms, from food poisoning to gas gangrene. . C. acetobutylicum, also known as the Weizmann organism, was first used by Chaim Weizmann to produce acetone and biobutanol from starch in 1916 for the production of gunpowder and TNT. Coxiella . Coxiella refers to a genus of Gram-negative bacteria in the family Coxiellaceae. . Coxiella burnetii is the only member of this genus. This organism is uncommon but may be found in cattle, sheep, goats and other domestic mammals, including cats and dogs. . Coxiella burnetii is the causative agent of Q-fever. . It is the most resistant bacteria in milk, thus parameter of heat process are determined for this bacterium. . Additionally, this bacterium can infect the people who are occupied with handling raw meat and packaging of meats.
Enterobacter . Gram (-) rods . They are common in nature especially on plants and crops. However, they can be found in water and intestinal tract. . They are members of coliform group. . The two important speciaes are E. aerogenes and E. cloaceae and they also can cause ropiness of milk. Enterococcus . Gram (+), non-sporeforming, some species are motile, non-capsulated, facultative anaerobic cocci . Some species are used as starter culture in cheese. . They are common in nature and their levels are high in fecal materials. Old nomenclature New nomenclature Streptococcus faecalis Enterococcus faecalis Streptococcus faecium Enterococcus faecium
Erwinia . Gram (-), catalase (-), anaerobic rods . This genus contains mostly plant pathogenic bacteria. . They break down the pectin in plants by protopectinase enzyme and cause to bacterial softening. . Erwinia carotovora: This bacteria is a plant pathogen with a wide host range (carrot, potato, tomato, leafy greens, squash and other cucurbits, onion, green peppers, etc.), able to cause disease in almost any plant tissue it invades. It is a very economically important pathogen in terms of postharvest losses, and a common cause of decay in stored fruits and vegetables. Decay caused by E. carotovora is often referred to as bacterial soft rot (BSR). Escherichia . Gram (-), short rods . Escherichia is a genus of Gram-negative, non-spore forming, facultative anaerobic, rod-shaped bacteria from the family Enterobacteriaceae. . Inhabitants of the gastrointestinal tracts of warm-blooded animals. . Escherichia species provide a portion of the microbially-derived vitamin K for their host. . It is not allowed the presence of this bacteria in foods. . There are four groups of E. coli: . Enteropathogenic E. coli (EPEC) . Enterotoxigenic E. coli (ETEC) . Enteroinvasive E. coli (EIEC) . Enterohaemorrhagic E. coli (EHEC)
Flavobacterium . Gram (-), non-motile, aerobic, non- sporeforming, catalase (+) rods. . They are common in soil and fresh water. . They can cause spoilage in refrigerated raw milk, meat and meat products and vegetables. Gluconobacter . Gram (-), obligate aerobic, catalase (+), oxidase (-) rods. . Some of them motile with polar flagella but some of them are non-motile. . They can spoil vegetables, fruits, bread yeast, beer, wine and vinegar. . The most important member of this genus is Gluconobacter oxydans. It is used for production of vitamin C.
Hafnia . Gram (-), facultative anaerobic and fermantative, oxidase (-), motile enteric rods. . They can spoil especially refrigerated meat and meat products. . Hafnia alvei is the only member of this genus. . H. alvei is a commensal of the human gastrointestinal tract and not normally pathogenic, but may cause disease in immunocompromised patients. . It can be found in soil, water, milk, sewage, human and animal feces. Halobacterium . Gram (-), catalase (+), obligate aerobic, some strains are facultative anaerobic, motile or non- motile, rod or cocci . Extremely halophilic bacteria . They need at least 15% salt for growth. The optimum salt concentration needed is 20-26%. . Halobacterium species produce pink, orange or red pigment. . They can spoil salted fish and meat products.
Halococcus . Gram (-), obligate aerob, oxidase and catalase (+), non- motile, double or tetrad sarcina or irregular cocci. . H. morrhuae, Halococcus dombrowskii, H. hamelinii, H. qingdaogense, H. saccharolyticus, H. salifodinae. Sediment tinted red by Halococcus. . They can spoil salted fish and meat products. Helicobacter . This genus has 31 species and identified firstly in 1982. . Some strains of this bacterium are pathogenic to humans as it is strongly associated with peptic ulcers, chronic gastritis, duodenitis, and stomach cancer. . Most important species pathogenic to humans: . H. pylori, H. cinaedi and H. fennelliae . It sources except humans haven’t been known yet. . It can spread by feces and can contaminate food, however, there isn’t any proof about its transmission to humans by foods.
Kurthia . Gram (+), non-sporeforming, obligate aerobic, motile rods . This genus has 3 species: . Kurthia zophii . Kurthia gibsonii . Kurthia sibirica . It can be isolated from feces of livestock. o . Its growth temperature range is wide: 5-35 C . Kurthia zophii is an indicator microorganism for frozen foods. . If frozen meats contain this bacterium, it can be concluded that the frozen meat was thawed and then frozen again. Lactobacillus . Lactobacillus is a genus of Gram-positive facultative anaerobic or microaerophilic bacteria. . Non-sporeforming and catalase (-) rods. . They are a major part of the lactic acid bacteria group, named as such because most of its members convert lactose and other sugars to lactic acid. . Many lactobacilli are unusual in that they operate using homofermentative metabolism (that is, they produce only lactic acid from sugars in contrast to heterofermentative lactobacilli which can produce either alcohol or lactic acid from sugars). . Why are they important for food microbiology?
Lactococcus . Lactococcus is a lactic acid bacterial genus of five major species formerly included as members of the genus Streptococcus Group N and related species. . Gram (+), non-sporeforming, non-motile, facultative anaerobic, catalase (-), oxidase (-) cocci. . They are homofermantative. . That is, they ferment the carbohydrates and produce lactic acid without producing gas (CO ). 2 L. lactis Leuconostoc Leuconostoc mesenteroides . Leuconostoc is a genus of Gram-positive bacteria, placed within the family of Leuconostocaceae. They are generally ovoid cocci often forming chains. . Gram (+), catalase (-), non-motile, facultative anaerobic cocci . Members of this genus are heterofermantative. . L. cremoris produces aroma compounds in milk products. It convert the acetaldehyde into ethanol, thus prevents formation of yoghurt aroma in butter.
Listeria . Listeria is a bacterial genus containing six species. Named after the English surgeon, Joseph Lister, Listeria species are Gram-positive bacilli and are typified by L. monocytogenes, the causative agent of listeriosis. . Listeria species: . Listeria monocytogenes, . L. ivanovii, . L. innocua, .L. monocytogenes is a . L. seeligeri, microaerobic and . L. welshimeri, o psycrotrophic (0-45 C) . L. grayii bacterium that can survive . L. monocytogenes is pathogenic to humans. low pH and high NaCl . It is commonly found in soil, stream concentrations. water, sewage, plants, and food. .Raw milk, cheese, ready-to- eat foods, meat and poultry products and seafood are play role in transmission. Micrococcus . Micrococcus is a genus of bacteria in the Micrococcaceae family. . Micrococcus occurs in a wide range of environments, including water, dust, and soil. . Micrococci have Gram-positive spherical cells ranging from about 0.5 to 3 micrometers in diameter and are typically appear in tetrads. . Mostly catalase (+), but some species are catalase (-).
Moraxella . Gram (-) short rods . They don’t produce acid form glucose, that is, they don’t do fermentation and have oxidative metabolism. Mycobacterium . Mycobacteria do not contain endospores or capsules, and are usually considered Gram-positive. . Most important species is M. tuberculosis. . Prevention of the transmission of tuberculosis by milk can be achieved by pasteurization of milk. M. tuberculosis. Paenibacillus . Paenibacillus is a genus of bacteria, originally included within Bacillus and Clostridium. . They are Gram(+) rods. . This genus has 11 new species. Pantoea . Pantoea is a genus of Gram-negative bacteria of the family Enterobacteriaceae. It comprises seven species and two sub- species. . Gram (-), non-capsulated and non-sporeforming, motile with peritrichous flagella, rod shaped bacteria. . They are commonly found in soil, water and human feces. Some of them are plant pathogens.
Pediococcus . Pediococcus is a genus of Gram-positive lactic acid bacteria, placed within the family of Lactobacillaceae. . Gram (+), catalase (-), microaerophilic cocci. . They usually occur in pairs or tetrads, and divide along two planes of symmetry. . They are purely homofermentative. . Most of them are used as starter culture in fermented products. . Pediocin? Propionibacterium . Gram (+), non-motile, anaerobic (but can tolerate oxygen), catalase (+), non-sporeforming rods. . P. freudenreichii subsp. shermanii is used for making emmental cheese. . When emmental cheese is being produced, P. freudenreichii ferments lactate to form acetate, propionate and carbon dioxide. . The products of this fermentation contribute to the nutty and sweet Emmentaler flavors of the cheese, and the carbon Country of Switzerland origin dioxide byproduct is responsible for Region, town Berne, Emmental forming the holes, or “eyes” in the Source of milk Cows cheese. Pasteurised Traditionally, no Texture hard Aging time 2-14 months depending on variety
Proteus . Gram (-), facultative anaerobic, motile, pleomorphic and short rod shaped bacteria. . Because of their high proteolytic activity, they can spoil meat, seafood and eggs which are stored at abusive temperatures. Pseudomonas . Catalase (+), Gram (-), aerobic, motile with polar flagella, rod shaped bacteria. . Some of the species are pathogenic to humans, animals and plants. . They can be primarily causative agent for spoilage of refrigerated meats, chicken meats, eggs and seafood. . Pseudomonas fluoresans produces green pigments on foods, while P. nigrificans black and the others brown pigments. . Although Pseudomonas aureginosa is a saprophytic species, it can also cause gastrointestinal diseases.
Psychrobacter . Gram (-), aerobic, non- motile, catalase (+), oxidase (+) coccobacilli. . They can not ferment glucose. . They can grow in media containing 6.5% NaCl and o at 1 C, however they can o not grow at 35-37 C. . They can be found in Species of Psychrobacter are found in the freezing waters and meats, poultry meats, fish icebergs of Antarctica. and waters. Salmonella . Gram (-), facultative anaerobic rods. . They are motile except the Salmonella Pullorum and Salmonella Gallinarum serotypes. . It is not allowed to presence of any members of this genus in foods. . This genus is belonged to Enterobacteriaceae family and has two species: . Salmonella enterica . Salmonella bongori . This genus has approximately 2300-2500 serotypes. . The most important serotypes are: Salmonella Typhi, S. Paratyphi, S. Typhimirium, S. Enteritidis. . S. Typhi and S. Parathyphi are the causative agent of typhoid fever and paratyphoid fever, while S. Typhimirium and S. Enteritidis cause gastrointestinal food-borne ilnesses.
Serratia . Serratia is a genus of Gram-negative, facultative anaerobic, rod- shaped bacteria of the Enterobacteriaceae family. . They produce red pigment on foods and on the surface of solid culture media. . Serratia liquefaciens and Serratia marcescens are the most important species. . Serratia marcescens can grow on meat and in milk producing red pigment. Shigella . Shigella is a genus of Gram-negative, non-spore forming rod- shaped bacteria closely related to Escherichia coli and Salmonella. . Non-motile, Gram (-), short rod . They can be found in dirty waters and intestinal tract of humans. . They are causative agents of various gastrointestinal diseases especially dysentery. . It can contaminate foods via dirty waters and humans. . This genus has four species which all are important for gastrointestinal diseases: . S. dysanteria . S. boydii . S. flexneri . S. sonnei
Staphylococcus . Staphylococcus (from the Greek: σταφυλή, staphylē, “bunch of grapes” and κόκκος, kókkos, “granule”) is a genus of Gram-positive bacteria. Under the microscope they appear round (cocci), and form in grape-like clusters. . Staphylococcus can cause a wide variety of diseases in humans and other animals through either toxin production or invasion. Staphylococcal toxins are a common cause of food poisoning, as it can grow in improperly-stored food. . The main classification of staphylococci is based on their ability to produce coagulase, an enzyme that causes blood clot formation. Streptococcus . Streptococcus is a genus of spherical Gram-positive bacteria belonging the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning easily bent or twisted, like a chain (twisted chain). Contrast this with staphylococci, which divide along multiple axes and generate grape-like clusters of cells. . Streptococci are oxidase and catalase-negative, and many are facultative anaerobes. . The most important species for foods is Streptococcus thermophilus. . Also some species can cause infections in upper respiratory tract.
Vagococcus . Gram-positive, catalase-negative and motile with peritrichous flagella. o o . They can grow at 10 C, but not at 45 C. . They can be found in fish, water, some other foods and feces. Vibrio . Vibrio is a genus of Gram-negative bacteria possessing a curved rod shape. . Typically found in saltwater, Vibrio are facultative anaerobes that test positive for oxidase and do not form spores. . All members of the genus are motile and have polar flagella. . Some species can not grow without NaCI and optimum NaCl concentration for growth is 3%. . V. costicola can tolerate the salt up to 23%. . The most important species are; . V. cholerae, . V. parahaemolyticus, . V. vulnificus
Weissella . Weissella is a genus of Gram-positive bacteria, placed within the family of Leuconostocaceae. The morphology of weissellas varies from spherical or lenticular cells to irregular rods . It was isolated firstly from a fermented Greek sausages in 1993. . Then, a new genus called Weissella was constituted by adding some Lactobacillus species. . They are Gram (+), non-motile, non-sporeforming, catalase (-), fermentative bacteria. Yersinia . Gram (-), oxidase (-), rods. . They are facultative anaerobic and thus can ferment glucose. . Yersinia pestis: bubonic plague (black death) . Yersinia pseudotuberculosis: septicemia . Yersinia ruckeri can cause diseases in salmon or some fresh water fish . Yersinia enterocolitica is the causative agent of human enteritis . Y. pseudotuberculosis and Y. enterocolitica may be transported to humans via foods, whereas Y. pestis is transmitted to host by flies or from the respiratory tract. o . They are psychotropic, thus can grow lower temperatures than 4 C, o although their optimum growth temperature is 28-30 C. . They can grow in refrigerated vacuum-packaged meats, boiled egg, sheep cheese, ice cream as well as oyster, raw shrimp, cooked lobster. Their incidence in pork and beef meat is rare.